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Synopsis : Titanium and its alloys are conventionally melted in watercooled copper hearth to avoid the chemical reaction between crucible and molten metal. However, titanium activity in TiAl is supposed to be low. This study was carried out to prove the possibility of vacuum-induction melting of TiAl alloys in highpurity CaO crucible. The following results were obtained. (1) Oxygen contents in TiAl were always 0.11•`0.14 wt% corresponded to thermodynamical equilibrium value when about 800 g was melted. This amount was a little larger compared with 0.04 wt% in plasma-arc melted TiAl. (2)Small amounts of 0.13•`0.15 vol% of CaO inclusions with the sizes of 1•`5ƒÊm were contained in TiAl, being nearly equal to killed steels. (3)New crucibles with 5•`20 wt% CaF2 for preventing CaO-TiAl reaction, showed no effect for decreasing oxygen content, but a usefull effect for reducing inclusions due to the thermal stress relief by CaF2 film between CaO particles, resulting in long durabilities. (4) As-cast TiAl with compositions of 33.5•`34.5 wt% Al showed elongations of 0.6-0.8% lower than plasma-arc melted TiAl. However, they were ameliorated to 1.1•`1.4% by annealing at 900•Ž to 1200 °C. This phenomenon can be explained from the point of veiw of the O diffusion from ƒÁ phase to ƒ¿2 phase.

TiAl Melting in CaO Crucible and Its Mechanical Properties